1. Field of the Invention
The present invention relates to a white organic light emitting device, and more particularly, to a white organic light emitting device which has high color temperature characteristics and improved change in color coordinates according to luminance change.
2. Discussion of the Related Art
Recently, as the information age has arrived in earnest, a display field to visually express electric information signals has rapidly developed. In order to satisfy such a trend, various flat display devices having excellent performance, such as a thin profile, a light weight, and low power consumption, have been developed and have quickly replaced conventional cathode ray tube displays.
Examples of the flat display devices include liquid crystal display devices (LCDs), plasma display panel devices (PDPs), field emission display devices (FEDs), and organic light emitting device (OLEDs).
Among the flat display devices, an organic light emitting device not requiring a separate light source, being compact and achieving clear color display is considered as an application having high competitiveness.
Such an organic light emitting device essentially requires formation of an organic light emitting layer, and in order to form the organic light emitting layer, a deposition method using a shadow mask has conventionally been used.
However, if the shadow mask is used in a large area, the shadow mask sags due to load thereof, and thus it is difficult to use the shadow mask multiple times, and an error occurs during formation of an organic light emitting layer pattern. Therefore, methods of replacing the shadow mask are required.
As one of the methods of replacing the shadow mask, a white organic light emitting display device is proposed.
Hereinafter, the white organic light emitting display device will be described.
The white organic light emitting display device is characterized in that respective layers between an anode and a cathode are deposited without a mask during the formation of light emitting diodes, i.e., organic films including an organic light emitting layer are sequentially deposited in a vacuum state by varying components thereof.
The white organic light emitting display device has various purposes, such as use in a thin light source, in a backlight unit of a liquid crystal display device, and in a full color display device employing color filters.
The white organic light emitting display device employs a phosphorescent/fluorescent stack structure in which a first stack using blue fluorescent elements as a light emitting layer and a second stack using red and green phosphorescent elements as a light emitting layer are stacked. Such a white organic light emitting display device produces white light by mixing blue light emitted from the blue fluorescent elements and red and green light emitted from the red and green phosphorescent elements.
However, a luminance change curve of blue light emitted from the blue fluorescent elements and a luminance change curve of red and green light emitted from the red and green phosphorescent elements are different, and thus color coordinates of the resulting white light are changed. Further, the fluorescent elements have poor internal quantum efficiency and thus have white color coordinate properties in which red is strongly displayed. Such a problem needs to be solved by applying an additional algorithm to a panel at a position in which the white coordinates are changed in a low luminance region.